1. Field of the Invention
The present invention relates to a magnetic recording/reproducing apparatus that is equipped with a magnetoresistive head that uses a spin-valve film as a magnetic sensor element for detecting magnetic signals while in contact with a magnetic recording medium.
2. Description of the Related Art
As magnetic sensor elements that detect the magnetic fields of signals from a magnetic recording medium, magnetoresistive elements (hereinafter referred to as MR elements) that utilize magnetoresistive effects where the resistance changes depending on the magnitude and direction of an external magnetic field are used. A magnetic head equipped with such an MR element is generally called a magnetoresistive head (hereinafter referred to as MR head).
As such an MR element, one in which anisotropic magnetoresistive effects are utilized has been in use conventionally, but because its magnetoresistance ratio (MR ratio) is small, an MR element which exhibits a greater MR ratio is desired, and in recent years, giant magnetoresistive elements (hereinafter referred to as GMR elements) that utilize spin-valve films have been proposed (see, for example, non-patent document 1 or patent document 1 mentioned below).
A GMR element has a spin-valve film in which a non-magnetic layer is held by and between a pair of magnetic layers, and utilizes so-called giant magnetoresistive effects where the conductance of a sense current flowing in-plane with respect to the spin-valve film changes depending on the relative angle of magnetization between the pair of magnetic layers.
Specifically, the spin-valve film has a structure in which an anti-ferromagnetic layer, a pinned layer whose direction of magnetization is pinned in a predetermined direction by an exchange-coupling field at work between itself and the anti-ferromagnetic layer, a free layer whose magnetization direction changes depending on an external magnetic field, and a non-magnetic layer for magnetically isolating the pinned layer and the free layer are stacked.
In a GMR element using a spin-valve film, when an external magnetic field is applied, the magnetization direction of the free layer changes depending on the magnitude and direction of the external magnetic field. When the magnetization direction of the free layer is opposite (anti-parallel) the magnetization direction of the pinned layer, resistance to the sense current flowing through the spin-valve film becomes greatest. On the other hand, when the magnetization direction of the free layer and the magnetization direction of the pinned layer are the same (parallel), resistance to the sense current flowing through the spin-valve film becomes smallest.
Therefore, in a magnetic head equipped with such a GMR element (hereinafter referred to as a GMR head), when a constant sense current is supplied to the GMR element, the voltage of the sense current flowing through the GMR element changes depending on the magnetic field of signals from a magnetic recording medium, and magnetic signals can be read from the magnetic recording medium by detecting the change in the voltage of the sense current.
In non-patent document 1, an example in which a GMR head is used in a hard disk drive is disclosed.
A hard disk drive has a structure in which, for example, a GMR head is mounted on a head slider attached to the tip of a suspension. The airflow that is generated by the rotation of the magnetic disk makes the head slider float above the signal recording surface of the magnetic disk, and reading operations with respect to the magnetic disk are performed by having magnetic signals that are recorded on the magnetic disk read by the GMR head mounted on the head slider.
Applications of the GMR head above are not limited to magnetic disk apparatuses, and in recent years, applications in magnetic tape apparatuses such as tape streamers and the like are being considered.
For example, a tape streamer that adopts a helical scan system has a structure in which a GMR head is positioned on the outer circumferential surface of a rotary drum such that it is oblique in accordance with the azimuth angle with respect to the direction that is substantially orthogonal to the running direction of the magnetic tape.
In the tape streamer, the magnetic tape runs obliquely with respect to the rotary drum, the rotary drum rotates, and reading operations for the magnetic tape are performed by reading the magnetic signals recorded on the magnetic tape while the GMR head mounted on the rotary drum and the magnetic tape slide in contact with each other.
In the tape streamer, because it is preferable that the distance between the GMR head and the magnetic tape, otherwise known as spacing, be kept small, in this respect, it is desirable that the surface of the magnetic tape be calendered.
However, as the surface of the magnetic tape becomes smoother, the contact area between the magnetic tape and the outer peripheral circumferential surface of the rotary drum increases, and the friction between the magnetic tape and the rotary drum while the tape is running becomes greater, thereby causing the magnetic tape and the rotary drum to stick, and it becomes difficult for the magnetic tape to run smoothly.
Therefore, the contact area with the outer circumferential portion of the rotary drum is made smaller, and the friction between the magnetic tape and the rotary drum smaller, by providing small protrusions on the surface of the magnetic tape using SiO2 fillers, organic fillers and the like.
In addition, a protective film, such as a DLC (diamond-like carbon) film or the like, for preventing damage or corrosion is formed on the surface of the magnetic tape.
In the conventional hard disk drive described above, reading operations are performed under conditions in which the GMR head is not in contact with the signal recording surface of the magnetic disk. In addition, Cu is ordinarily used for the non-magnetic layer of the spin-valve film, and on the surface of the GMR head that faces the magnetic disk is formed a protective film, such as a DLC film or the like, for preventing Cu from becoming corroded.
On the other hand, as for the magnetic recording tape medium, so-called coated type magnetic recording media have been widely used. To make this type of magnetic recording medium, powder magnetic material such as oxide magnetic powder or alloy magnetic powder is dispersed in an organic binder such as vinyl chloride-vinyl acetate copolymer, polyester resin, polyurethane resin etc., and a magnetic coating material thus prepared is coated on a non-magnetic substrate and is dried.
In contrast, with the increasing demand for high-density recording, a magnetic recording medium of the so-called metal magnetic thin film type has been proposed and is drawing attention. To make this type of magnetic recording medium, a metal magnetic material such as Co—Ni, Co—Cr, Co, etc. is directly deposited on a non-magnetic substrate by plating or by vacuum thin film forming means (such as vacuum deposition, sputtering, ion plating and the like)
The magnetic recording medium of the metal magnetic thin film type is superior in terms of coercivity, residual magnetization, and squareness ratio. It has superior electromagnetic conversion characteristics at short wavelengths, and the thickness of the magnetic layer can be made very thin. As a result, it is advantageous in that thickness loss at reproduction and recording demagnetization are low. There is no need to use a binder, which is a non-magnetic material, into the magnetic layer, and the filling density of the magnetic material can be increased and higher magnetization can be attained.
Further, in order to improve the electromagnetic conversion characteristics of such magnetic recording media and attain higher output, so-called oblique vacuum deposition has been proposed where the magnetic layer is obliquely deposited in forming the magnetic layer of the magnetic recording medium. The magnetic recording medium of this type has been put to practical use as a magnetic tape for high definition VTR or for digital VTR.
[Non-Patent Document 1]
“Giant Magnetoresistance in Soft Ferromagnetic Multilayers” Physical Review B, Volume 43, Number 1, pages 1297˜1300
[Patent Document 1]
Japanese Patent Application Publication Hei-8-111010